Assessment of pearl millet genotypes for drought stress tolerance at early and late seedling stages

Pearl millet is one of the most important C4 panicoid millet crops grown in dry and arid regions of India and West Africa. Drought is one of the major limitations to its growth potential. Therefore, selection of drought-tolerant cultivars through in vitro screening can be an important approach for crop improvement programmes. An experiment was conducted on six pearl millet genotypes with two different levels of osmotic stress treatments, i.e., control and 20% polyethylene glycol (PEG) 6000 at early seedling stage for eight seedling traits and proline content, while 30% PEG at late seedling stage for proline and malonaldehyde (MDA) content and gene expression analysis. Analysis of variance (ANOVA) showed significant treatment effects on all early seedling traits with respect to treatment x varietal interaction. Our results showed a relative decline for different seedling traits in individual genotypes with increased osmotic stress. TT-1 showed a maximum reduction in almost all traits while the minimum decline was noted in PRLT2/89-33. Further, proline and MDA accumulation in control and 30% PEG-6000-treated seedlings at late growth stages were in confirmation with the observations recorded at early seedling growth stages. Expression analysis using quantitative real-time (qRT)-PCR of three antioxidative genes namely, ascorbate peroxidase (APX), glutathione reductase (GlutR) and superoxide dismutase (SOD) also confirmed higher osmotic stress tolerance of PRLT2/89-33 seedlings. Overall results suggested that selection for any of the above traits at early or late-seedling growth stages may prove useful for crop improvement programs directed towards developing stress-tolerant cultivars.